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The Amazing Short-circuit Finding Brush: An Electronic Detective – Part I

Introduction and Specifications

The Situation

Imagine staring down the multi-faceted green spider web of electrical interconnections known as the circuit board in your hands, searching frantically for an answer. 

After a long pause you ask yourself, “just where does pin 7 of IC 3 ultimately connect to?” 

We can all relate to that, no? 

Perhaps not. 

For those of us in the electronic repair and PCB reverse engineering industry, however, challenges like this are a (perhaps quirky) daily reality.

Whether we are repairing your servo motor or reverse engineering electronics to re-engineer your industrial PLC control board, we need to identify the electrical connections. In simple designs we can easily trace the circuits with a quick visual inspection. Things get more complicated, however, when the wires start weaving in and throughout the circuit board. 

That’s why, sometimes, tracing the connection to pin 7 of IC 3 might be more comparable to finding a needle in a haystack.

The Solution

Enter: the Short Finder.

What is that, you might ask?

Short finders are some of the most useful tools for electronic reverse engineering and PCB repair in the lab.

A short finding tool identifies whether two or more points in a circuit are (or are effectively) connected directly together. Think of a wire connecting two ends of a cable. With this tool we can identify all electrical connections without needing to see where every wire actually runs.

When further equipped with a brush on one end and a pinpoint probe on the other, the tool allows us to probe that same pin 7 of IC 3 and find all of its other connection points by a simple sweep of the brush across the PCB.

In the haystack analogy, the short finding brush is like a magnet that casually picks out all the needles that we are seeking and ignores all else.

The Supply

You might be wondering, “where can I get my hand on one of these?”

Brush-equipped short finding devices have been commercially available in the past but are now quite hard to find. 

That’s why we teamed up with students from Mohawk College here in Hamilton, Ontario to redesign an EPIC ENA Handheld Short Finder Brush. Our entire team now has access to this tool. We find that it can boost productivity, allowing us to provide even better turnaround times!

We have decided to release the EPIC ENA Handheld Short Finder Brush as open source hardware. After a small series of posts, starting with this one, you will have everything you need to build your very own electronic circuit detective!

The Specifications

For those more technical among us, the main giveaway of this first post is our design specifications for the tool.

The Output Voltage

Approximately 0.5 VDC is output at the probes, waiting to be shorted out

The Source Current

Maximum Output current limited to approximately 100uA; low current limit prevents any possible damage to circuit under test

The Continuity Threshold

Internally adjustable; approximately 4-43; tool audibly indicates a short circuit when resistance between the probes is less Thant the chosen threshold

The Brush

Phosphorus Bronze bristles with stainless steel housing; easy to replace; bristles are projected by adjustable plastic slider

The Power Source 

1X Lithium- Ion 3.7/4.2V, 300mAh rechargeable battery; charges via USB-C connector; does not need to be opened to change the battery; battery life is 30 hours

The Power Switch

Momentary tactile switch, short press to turn on; long press and hold to turn off

The Takeaway

Here at ENA Electronics in Hamilton we are always looking for ways to improve our industrial repair and reverse engineering processes, including developing custom in-house tools.

We also enjoy offering neat insights into our services and keeping the dialogue open with our clients and the broader electronics community.

Stay tuned for Part II, where we will dig into the case design and compare our tool to an existing product!

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